Patent GB-313559-A (GB)
Title: Improvements in or relating to regulating transformers
IPC: H01H9/00
Filed: 1929-05-23
Abstract: 313,559. Siemens - Schuckertwerke Akt.-Ges. Juna 14, 1928, [Convention date]. Regulating transformers.-In transformers of the type in which a tapped winding is associated with a pair of regulating switches which are operated in turn while the load current is diverted by means of a main switch, at least one auxiliary winding either inductively associated with the main transformer or forming the secondary of an auxiliary transformer is associated with the main switch contacts, the voltage produced by the winding being such that one of the contacts of the main switch is brought to a potential lying between that of two adjacent tappings whilst the current flowing in the circuit of the auxiliary winding opposes the main load current so as to relieve the main switch current so as to relieve the main switch contacts of current at the moment of break. From the position shown in Fig. 1 in which the full voltage of the transformer secondary 2 is available at the load terminals 26, voltage is reduced by the following sequence of operations. Main switch 500 is rotated away from contact 502, thus diverting load current from regulating switch 100. The latter is simultaneously shifted through gearing 101, 102, 103 to top position 22. When main switch 500 occupies position indicated by broken lines, the circuit of auxiliary winding 3 which is inductively associated with the main windings of the transformer, is completed through resistance 505 and inductance 506. The auxiliary winding 3 produces a current, indicated by dotted lines, equal in value and, at the contact 503, in the opposite direction to the load current indicated in full lines. Thus the movement of the main switch contact 500 may be continued away from the contact 503 without arcing. Moreover the voltage of the auxiliary winding 3 is such as to lower the potential of the contact 504 to a value between that of contacts 501, 503 that are now connected through their respective regulating switches 100, 200 to different tap positions. With the main switch on contact 504, the load circuit voltage is reduced to a corresponding intermediate value. Further movement of the main switch connects the load circuit through contact 501 and regulating switch 100 to the tap position 22. Movement of the main switch away from contact 504 causes, through gearing 201, 202, 203, the regulating switch 200 to be shifted to tap position 22 while the load current is diverted through regulating switch 100. Main switch 500 is then moved forward to the original position to connect the circuits of the two regulating switches in parallel to tap position 22. The required phase relationship between the voltage of the winding 3 and that of the main winding 2, viz., a difference of 90, may be obtained in a three-phase transformer by dividing the auxiliary winding into two parts, arranged in the core limbs corresponding to the other two phases. As shown in Fig. 2, the auxiliary winding for phase S comprises the parts 3<a>, 3b inductively associated with the windings of phases R, T but spaced away therefrom to obtain high dispersion. A further lag approximating to 90 is produced between the current and voltage in the circuit of the auxiliary winding owing to the inductive nature of that circuit, thus obtaining a phase displacement approaching 180 between the main load current and the current produced by the auxiliary winding. The Specification also comprises a modification in which two auxiliary windings adapted to give two intermediate values of voltage between each tap position are associated with a spring-actuated main switch giving a quick change-over from contact to contact without bridging the intermediate contacts.